There is often confusion between the goals, authorities and roles of Change and Release Management. In fact, the objectives of each of process are very, very different.
Change rules! Change Management is an authoritative process that governs anything that potentially impacts a new or existing service. It is both the enabler of innovation and protector of stability. It is first and foremost a risk management process. It is also a planning process.
If Change Management is a governance process, Release Management is an action process. Under the authority of Change, Release builds, tests and releases new or updated services into the production environment. Every release is comprised of a single change or package of changes. Release Management is more technical than Change.
If done well, both processes will avoid unnecessary levels of bureaucracy and will build a collection of change and release models that pre-define and pre-approve the rigor required based on levels of risk. The more mature the processes, the higher number of standard changes. Approaches such as Agile and DevOps help to limit over processing while improving the flow of all changes from concept to operation.
A learner recently asked about the relationship between projects, the PMO and Change/ Release Management. Remember, that Change and Release Management are only processes – on their own they do nothing – they must be executed by people. Every project will likely spawn multiple changes to infrastructure, applications and/or documentation. Each change will either be unique or fall within the bounds of an existing change model. Releases emanating out of the project can be handled singularly, sequentially or packaged together when it makes sense. Since the PMO will manage the project, I would expect that the PMO would similarly request and manage the changes.